I am building a simple game where 2 people can duel against each other. I am using GameSparks as a back end. My problem is, that whenever player #1 casts a spell that is channeling, player #2 can see the channeling only when his screen is turned on and in focus.

Whenever player's #2 screen turns off, the app is not active anymore so the spell is not being casted at him. When player #2 turns on the screen, the channeling starts, but player #1 was already done channeling a while ago.

I assume that is related to the way Android system works. It puts apps that are not in focus on pause.

My problem now is, how can I make sure that player #2 gets a notification whenever he is hit by the spell without a need to use any third party service to keep the app alive (to avoid huge battery consumption) and also without a need to use push notifications (as from what I've heard, if there is a high load, the push doesn't happen right away, since there is a queue)